Electroforming is the electrolytic deposition of dimensionally stable metal layers on a substrate. Invented in 1838 by Jacobi in Russia, this technique was adapted for use in dentistry in 1856 by Newell. The use of this technique in dentistry was greatly expanded by the work of O. W. Rogers, who patented an apparatus and method of electroforming dental crowns in U.S. Pat. No. 4,288,298. The development of nontoxic plating solutions having high penetration power made it possible to produce porcelain fused to gold dental restorations where the gold deposition is of a precise and uniform thickness. This application was limited to a single crown, however, until the development of the cast metal pontic technique for bridges, and the 24 K gold was electroformed over the metal and abutments. The result was a multilayer metal bridge having sufficient stability for multiple units, that is, a bridge which spans multiple teeth. Two articles which discuss the use of electroforming in this way are "Electroforming as an Alternative to Full Ceramic Restorations and Cast Substructures" by Ronald M. Stewart, published in Trends and Techniques in the Contemporary Dental Laboratory, April 1994:42-47 and "Electroforming Technology for Ceramometal Restorations" by Tonino Traini, published in Quintessence of Dental Technology, 1995: 21-28. Gramm Technology, of Woodbridge, Va. and Tiefenbronn, Germany both manufacture dental systems for electroforming gold and related products. The founder of Gramm Technology, Gerhard Gramm, has several U.S. and foreign patents in this area, including U.S. Pat. No. 5,173,161, which describes a device for electroforming work pieces and WO 9207977, which describes a device for coating workpieces used in the dental field.
Electroformation is also used in dentistry as a casting method to produce accurate dental prostheses, as described in U.S. Pat. No. 5,316,650, to Ratzker et al. This technique uses a metallic glass alloy containing cobalt and phosphorus. U.S. Pat. No. 4,451,639, to Prasad describes special metallic ceramics which have been developed for use in the electroforming process. The ceramic of Prasad contains many metals, including palladium, cobalt, gallium, gold, aluminum, copper, zinc and ruthenium or rhenium. Additionally, electroforming is used in other manufacturing methods beyond dentistry. For example, U.S. Pat. No. 5,393,405, to lacono et al., discusses the production of jewelry using electroformation of multiple layers of gold where the layers differ in hardness.
Ceramic restorations have long been an alternative to metal structures, having vastly superior aesthetics and perfect biocompatibility. Developments in high strength ceramics, that is, ceramics having a flexural strength greater than 300 megapascals (MPa), have made all-ceramic bridges possible. Such high strength ceramic is necessary for producing the coping portion of the all-ceramic restoration. In particular, as described in U.S. Pat. No. 5,695,337 to Sadoun, a ceramic formulation containing multiple metal oxides displays the desired strength. The amount of Al.sub.2 O.sub.3 has been increased to 85% by weight in a commercial product known as In-Ceram, produced by VITA Zahnfabrik H. Rauter GmbH & Co., Bad Sackingen, Germany. This ceramic has a strength of 600 MPa and functions well in single units and anterior bridges. The general method of using this material is reported in "Working with the In-Ceram Porcelain System" by Harry Levy and Xavier Daniel, published in Prothese Dentaire 44-45 45: June-July 1990. A further discussion of this technique can be found in "A renaissance of ceramic prosthetics?" by Norbert Futterknecth and Vanik Jinoian, published in Quintessence of Dental Technology, special reprint, 1992. The inceram zirconia high strength ceramic (AL.sub.2 O.sub.3 --ZrO.sub.2) has considerably improved mechanical characteristics. This makes posterior bridges possible. Due to the increased opacity, however, there are aesthetic limitations.
Each of these dental systems have serious drawbacks. Metal-base restorations have biocompatibility problems, often reflected as gingival degeneration, which reveals a dark metal margin on the restored tooth which ruins the aesthetic appearance of the restoration. Metal has poor thermal conductivity qualities and can corrode over time. The preparation of metal copings often involves toxic metals which present environmental problems for the dental office personnel and during disposal. Ceramic restorations, when of sufficient strength for posterior bridgework, are too opaque to provide good aesthetics. The present invention has solved these problems by providing a restoration which does not contain materials which cause reactions in the body, do not promote temperature sensitivity, and are relatively non-toxic. Additionally, the present invention provides vivid aesthetics with the warm color of the 24 K gold deposition, and of all the alloys, 24 K gold is highly biocompatible.